Reap unvalidated networks that have no chance of becoming highest scoring.

These networks are unneeded and waste battery.  We won't bring up these
networks in the first place if they have no chance of becoming highest scoring.
This change handles the case where these networks are already up and
transition to a state where they have no chance of becoming highest scoring.
This happens when another network validates with a score higher than this
network can ever hope to attain.

bug:18489123
Change-Id: I77a96a72e250e25e44e0c50e7a928af8b35bb6ab